Evolutions of Crystal Structure, Stoichiometry and Electrochemical Behavior with Co Substitution in LiNi1-yCoyO2 Positive Electrodes

LiNi1-yCoyO2（0.1 ≤ y ≤ 0.4） positive electrode materials are synthesized by a chemical method with stoichiometric acetates of related cations. Their crystal structure, stoichiometry and electrochemical behaviors versus Co concentration are investigated by x-ray diffraction, synchrotron-based x-ray absorption fine structure and galvanostatic cycling ts. The results reveal that the non-stoiehiometric Ni^2＋, Li/Ni cation mixing and polarization are reduced as the amount of Co substitution increases, clearly indicating that the Co element is a medium for easily oxidizing Ni^2＋ to Ni^3＋ during the synthesis process.